I don't believe you can animate the alpha value of an image, and we don't have access to an the thumb's image view (if it has one) to animate its alpha. One thing you can do is add an image view as a subview of the slider, and make it slightly bigger than the thumb image, and animate its alpha value (it will be behind the thumb's image, so it will show up as a pulsating ring). In this example, I set the image view's frame in thumbRectForBounds:trackRect:value:, and cancel the animation in touchesBegan,